@Donna130
Well you certainly need to go to the property - if the guests have left with their possessions then fine - get the place ready for next guests and leave an accurate review (assuming they were tidy, it was just their communication that was poor). But if their possessions are still there - you must contact Airbnb immediately and I would have a witness with you - carefully move their things (take a photograph first) into the kitchen area and explain to new guests when they check in that you will be removing the items that afternoon.
If Airbnb don't respond, then box up the items and leave another message as to where the items can be collected and will be kept safe until such time.
Most probably the guests will turn up - but the one in a million shot is that something may have happened - so collect their things and move on with looking after new guest.
If you only use keys -- think of getting a combination smart lock so something like this doesn't make things extra difficult.
Best of Luck - - and do let us know what happens!
Best Wishes